Android程序間通訊——ContentProvider的使用
前言
ContentProvider作為四大元件之一,一直以來存在感都很低,但其實它的功能還是很強大的,尤其是在實現程序間通訊的時候。和AIDL一樣,ContentProvider的底層實現也是Binder,但是由於系統已經為我們做了封裝,所以它的使用過程要簡單的多。
一、什麼是ContentProvider?
內容提供者,是Android
四大元件之一。是Android中提供的專門用於不同應用間進行資料共享的方式,它天生就適合程序間通訊。
二、為什麼要使用ContentProvider?
通常我們的軟體系統架構肯定會包含業務和資料,為了降低上層業務對底層資料的依賴,需要增加一個數據訪問層來進行解耦,而Android系統為我們提供的
三、ContentProvider支援哪些資料來源?
ContentProvider僅僅充當一箇中間者角色,可以說是資料的“搬運工”,真正操作的資料來源可以是Sqlite資料庫、檔案、XML和網路等。
四、如何使用ContentProvider?
1、建立一個自定義的ContentProvider
- 繼承ContentProvider類並實現六個抽象方法:onCreate、getType、query、insert、delete和update
- 在onCreate中做初始化;getType用來返回一個Uri請求所對應的MIME型別,可以是視訊、圖片等,如果不關心型別可以直接返回null或者“*/*”;其餘四個方法則對應對資料表的增刪改查功能
2、在AndroidManifest中註冊這個ContentProvider
- android:authorities必須是唯一的,它是這個ContentProvider的唯一標識
- 設定訪問許可權,可分為讀許可權和寫許可權
3、在ContentProvider中初始化資料來源,例如建立一個數據庫等
4、通過唯一標識就可以呼叫ContentProvider了
五、需要注意什麼?
1、在ContentProvider的六個方法中,除了onCreate由系統回撥並執行在主執行緒中,其它方法均由外界回撥病執行在Binder執行緒池中;
2、android:authorities必須是唯一的;
3、ContentProvider的許可權可以分為讀許可權和寫許可權,外界也必須宣告對應的許可權,否則外界呼叫時應用會異常終止;
4、query、insert、delete和update四大方法是存在多執行緒併發訪問的,因此方法內部要做好執行緒同步;
5、操作資料庫時一定要注意SQL語句的正確,否則程式將無法啟動。特別注意空格和括號!
六、程式碼怎麼寫?
首先還是要宣告一下,我這篇文章主要是《Android開發藝術探索》的讀書總結,所以這裡關於程式碼的部分,我是直接照著書上敲了一遍,主要是想了解使用ContentProvider的整個流程,其實真正自己敲的時候才會發現問題,然後才能更好更快的掌握,如果你是初次學習ContentProvider,一定要自己敲一遍程式碼!!!
1、建立一個BookProvider繼承ContentProvider
public class BookProvider extends ContentProvider {
private static final String TAG = "BookProvider";
private static final String AUTHORITY = "com.example.kangbaibai.bookprovider.BookProvider";
private static final Uri BOOK_CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/book");
private static final Uri USER_CONTENT_URI = Uri.parse("content://" + AUTHORITY + "/user");
private static final int BOOK_URI_CODE = 0;
private static final int USER_URI_CODE = 1;
private static final UriMatcher sUriMatcher = new UriMatcher(UriMatcher.NO_MATCH);
static {
sUriMatcher.addURI(AUTHORITY, "book", BOOK_URI_CODE);
sUriMatcher.addURI(AUTHORITY, "user", USER_URI_CODE);
}
private Context mContext;
private SQLiteDatabase mDb;
@Override
public boolean onCreate() {
Log.e(TAG, "onCreate: current thread:" + Thread.currentThread().getName());
mContext = getContext();
//ContentProvider建立時,初始化資料庫。注意:實際使用中不推薦在主執行緒中進行耗時的資料庫操作
initProviderData();
return true;
}
private void initProviderData() {
mDb = new DbOpenHelper(mContext).getWritableDatabase();
mDb.execSQL("delete from " + DbOpenHelper.BOOK_TABLE_NAME);
mDb.execSQL("delete from " + DbOpenHelper.USER_TABLE_NAME);
mDb.execSQL("insert into book values(3,'Android');");
mDb.execSQL("insert into book values(4,'IOS');");
mDb.execSQL("insert into book values(5,'HTML5');");
mDb.execSQL("insert into user values(1,'jake',1);");
mDb.execSQL("insert into user values(2,'jasmine',0);");
}
@Nullable
@Override
public Cursor query(@NonNull Uri uri, @Nullable String[] projection, @Nullable String selection, @Nullable String[] selectionArgs, @Nullable String sortOrder) {
Log.e(TAG, "query: current thread:" + Thread.currentThread().getName());
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported Uri: " + uri);
}
return mDb.query(table, projection, selection, selectionArgs, null, null, sortOrder, null);
}
@Nullable
@Override
public String getType(@NonNull Uri uri) {
Log.e(TAG, "getType: current thread:" + Thread.currentThread().getName());
return null;
}
@Nullable
@Override
public Uri insert(@NonNull Uri uri, @Nullable ContentValues values) {
Log.e(TAG, "insert: current thread:" + Thread.currentThread().getName());
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported Uri: " + uri);
}
mDb.insert(table, null, values);
mContext.getContentResolver().notifyChange(uri, null);
return uri;
}
@Override
public int delete(@NonNull Uri uri, @Nullable String selection, @Nullable String[] selectionArgs) {
Log.e(TAG, "delete: current thread:" + Thread.currentThread().getName());
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported Uri: " + uri);
}
int count = mDb.delete(table, selection, selectionArgs);
if (count > 0) {
mContext.getContentResolver().notifyChange(uri, null);
}
return count;
}
@Override
public int update(@NonNull Uri uri, @Nullable ContentValues values, @Nullable String selection, @Nullable String[] selectionArgs) {
Log.e(TAG, "update: current thread:" + Thread.currentThread().getName());
String table = getTableName(uri);
if (table == null) {
throw new IllegalArgumentException("Unsupported Uri: " + uri);
}
int row = mDb.update(table, values, selection, selectionArgs);
if (row > 0) {
mContext.getContentResolver().notifyChange(uri, null);
}
return row;
}
private String getTableName(Uri uri) {
String tableName = null;
switch (sUriMatcher.match(uri)) {
case BOOK_URI_CODE:
tableName = DbOpenHelper.BOOK_TABLE_NAME;
break;
case USER_URI_CODE:
tableName = DbOpenHelper.USER_TABLE_NAME;
break;
default:
break;
}
return tableName;
}
}
2、註冊該ContentProvider
<provider
android:name=".BookProvider"
android:authorities="com.example.kangbaibai.bookprovider.BookProvider"
android:exported="true"
android:process=":provider" />
3、建立資料庫
public class DbOpenHelper extends SQLiteOpenHelper {
static final String DB_NAME = "book_provider.db";
static final String BOOK_TABLE_NAME = "book";
static final String USER_TABLE_NAME = "user";
static final int DB_VERSION = 1;
private String CREATE_BOOK_TABLE = "CREATE TABLE IF NOT EXISTS "
+ BOOK_TABLE_NAME + "(_id integer primary key," + "name TEXT)";
private String CREATE_USER_TABLE = "CREATE TABLE IF NOT EXISTS "
+ USER_TABLE_NAME + "(_id integer primary key," + "name TEXT,"
+ "sex INT)";
public DbOpenHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK_TABLE);
db.execSQL(CREATE_USER_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
}
4、在Activity中呼叫
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Uri uri = Uri.parse("content://com.example.kangbaibai.bookprovider.BookProvider");
// getContentResolver().query(uri, null, null, null, null);
// getContentResolver().query(uri, null, null, null, null);
// getContentResolver().query(uri, null, null, null, null);
Uri bookUri = Uri.parse("content://com.example.kangbaibai.bookprovider.BookProvider/book");
ContentValues values = new ContentValues();
values.put("_id", 6);
values.put("name", "程式設計的藝術");
getContentResolver().insert(bookUri, values);
Cursor bookCursor = getContentResolver().query(bookUri, new String[]{"_id", "name"}, null, null, null);
if (bookCursor != null) {
while (bookCursor.moveToNext()) {
Book book = new Book();
book.bookId = bookCursor.getInt(0);
book.bookName = bookCursor.getString(1);
Log.e(TAG, "query book: " + book.toString());
}
bookCursor.close();
}
Uri userUri = Uri.parse("content://com.example.kangbaibai.bookprovider.BookProvider/user");
Cursor userCursor = getContentResolver().query(userUri, new String[]{"_id", "name", "sex"}, null, null, null);
if (userCursor != null) {
while (userCursor.moveToNext()) {
User user = new User();
user.userId = userCursor.getInt(0);
user.userName = userCursor.getString(1);
user.isMale = userCursor.getInt(2) == 1;
Log.e(TAG, "query user: " + user.toString());
}
userCursor.close();
}
}
}
結語:
到此一個簡單的ContentProvider程式就搞定了,本文只是簡單做個讀書總結,之後我會繼續深入瞭解ContentProvider原理,希望大家支援~
程式碼已上傳至github:https://github.com/kb18519142009/ContentProvider
歡迎star~